Can i use 1/2 watt?

[12AX7]

cathode resistors on my EL34's that is. I use 1 ohm resistors to check bias across, but all i can find are 1/2 watt at 1% tolerance. I can't see what it would matter, but i saw i think it was ceritone using 2-3 watters in a layout and figuring he knows more theory than me, maybe theres a reason not to use 1/2 watts there.

[The_Gaz]

I may be wrong, but I think that they may be over-rated so that they don't open up if there is a tube failure and the current runs away. It may actually save your butt, which is why some companies fuse the cathodes of the power tubes, but it's not reliable (to use a resistor as a fuse). If the amp is properly fused, the fusing of the cathodes is likely not needed, and the lower wattage ones opening up during a tube failure may save nothing and just be an annoyance to replace.

[sluckey]

Doug has 1 ohm, 1 watt, 1% tolerance resistors.

You would have to have 500ma flowing thru a 1Ω resistor to dissipate 1/2 watt. You could safely pass 250ma thru that half watter.

 

[12AX7]

Thanks. I'll do the 1/2w then. Appriciate it.

[ckilgore]

You would have to have 707ma flowing thru a 1Ω resistor to dissipate 1/2 watt.

[sluckey]

You would have to have 707ma flowing thru a 1Ω resistor to dissipate 1/2 watt.

Yep, you're right. Sorry 'bout that.   

P = I²R

[stratele52]

I use always 1/2 watt resistor

[G._Hoffman]

If there is a short somewhere, you WANT it to fail.  That way, it will burn up and act as a fuse, hopefully keeping your PT intact.

Or at least, that is the rational I've always heard, and it makes some sense to me.


Gabriel

[stingray_65]

Big resistors are easier for my eyes to see

Those tiny precision 1/4W metal films with 5 color bands make me look for my DMM every time!

The one thing I really think CC resistors are great for.. easy to read! the brown bodies contrast the colors best!

Ray

[12AX7]

If specs call for 1 watt and all you have are 1/2 watts, then take 4 of those puppies and wire them series/parallel.  Very ugly, but it works most of the time. 

problem is, if you start doing that the tolerance can multiply and theres goes your 1% tolerance. No matter tho, as i found some dale 1%'ers at a local surplus. They're 10 watt if i recall, (the metal chassis mount kind) but thats all i could find.

[sluckey]

Why didn't you use the 1/2 watters? Or order some 1 watters from Doug?

[12AX7]

Don't need anything i could think of besides that, and shipping is $7.15.